I found an old
@Sanglier post saying this was designed by the same designer (or one of the designers) that worked for wilson on the Prostaff? That's cool as hell IMO.
You did very well on this e-GW pickup. It is one of my favorites.
Yes, these Power Tech frames were the brainchild of Rich Janes, a prolific designer who began his career in the late '60s at Bancroft, who was still active in the industry consulting for Babolat and ASICS just a few years ago. Other than working on the PS series when he was at Wilson, he was also responsible for the loose-bridge Spalding Arista design, the fused-halves NXG design at Prince that ultimately gave rise to the O-ports, and many more unconventional mousetraps that were once welcomed by the industry. However, Janes would also be the first to tell you that the DIB layout is a gimmick, that it was intended to draw attention rather than to solve a real problem. These racquets were completed in 1986, just as Spalding was about to take a break from tennis (before mounting a massive and final comeback in 1988), so the timing could not have been worse. There was virtually no effort to promote these frames, which vanished from the market shortly thereafter.
I actually think Janes' assessment of his unloved brainchild is needlessly dismissive. Yes, the whole idea of shortening the central mains relative to the peripheral ones to increase the sweet spot is more than a little hooey, given that there are many other designs that do the exact opposite (by increasing the length of the central mains to the maximum permitted under existing rules) that suffer no ill effect at all. But Janes wasn't the first to do this, and there were plenty of much dumber gimmicks that were green-lighted by other vendors. The basic fact is, if you struck the ball away from the central axis, the result would be sub-optimal regardless of string length differential, because other factors such as frame twist and vibration characteristics would also come into play, which are far more consequential than strings that are an inch longer or shorter in one direction or the other. However, if you MUST make the central mains shorter than the peripheral ones for any reason, then DIB is the best way to do it by far.
A bridge is typically convex against the direction of the load because it's the most efficient way to spread that load, turning tension into compression, minimizing stress and wear on the support structures. It is the reason all those Roman arches are still standing after millennia. This notion has become such an ingrained part of our intuition that even a completely flat bridge would make us go - Hmm, this thing doesn't look quite right; is it strong enough to hold up? I don't think any of us would knowingly walk or drive onto an unsuspended bridge that droops significantly in the middle without some very extreme incentives.
This is why Rossignol's inverted bridge looks "broken", or at least "very likely to break" even to someone who hadn't thought about the physics behind it. Indeed, the very fact that it is called "inverted" is
prima facie admission that it is arched the wrong way. The amount of reinforcement required to keep the bridgeheads intact on such a bridge far exceeds that of a conventional bridge. However, on the Power Tech double bridge design, only the outer bridge is truly load-bearding, and this bridge is arched in the
correct direction! The inner bridge is just there to reduce string length, a job requiring very little strength. The crossing of the strings in the gaps between the bridges is meant to further ensure that they behaved like shorter strings, and not longer strings extending through a passive element, like the kind found on the Fox "WB-215", the Sp.In long string, and many similar "strung-thru-the-bridge" designs.
In short, if you intended to make a string bed that looked and behaved like a double-headed axe, this is the most (only?) physically-sound way to do it. The benefit behind the design may be dubious, but Janes' execution was flawless!
When asked why these frames played so well, if DIB were nothing more than gimmicky nonsense, Janes replied: "Probably because the extra bridges put a lot of extra mass where it mattered". So there is that.
In a way, Tacchini revisited these ideas many years later, either independently or through inspiration, and came up with a far more subtle, and almost sensuous (if the term can ever be applied to racquet aesthetics) design that they appropriately named 'Cygnus', which also played quite well, possibly for the same reasons Janes proposed.
